Constant-voltage system.



T. SPENCER.

CONSTANT VOLTAGE SYSTEM.

APPLICATION FILED DEC-1. 1913.

1,220,370. Patented M21127, 1917.

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To all whom it may concern:

Be it known that I, THOMAS SPENCER, a citizen of the United States, residing at Philadelphia, in the county of Philadelphia 6 and State of Pennsylvania, have invented a certain new and useful Improvement in Constant-Voltage Systems, of which thefollowing is a full, clear, and exact description.

This invention relates to a constant voltage system with varying speed of the prime mover. It is primari y intended for car Ii hting but. can be used' advantageously 'w erever the speed of the prime mover varies to a considerable extent. The invention will be'described witlli {)eferencefto a Oil! li ti stem but on y yway 0 exam e. ihni 03. 1 car lighting system should, with p out any adjustments whatever give constant unidirectional volta at all speeds between wide limits, regardfe ss of the direction in whichthe car is moving. The object of my iniilitionlisito 3060l1npliSh this result;

e v0 tage eve oped n a genera 1' armature follows the wellknown law,

where Bis the field strength, N the speed of-the armature, and k-a constant. I If by some means the field flux can be made to so vary inversely as the speed, the voltage induoed wouldbe constant. That 1s, if

' the above equationwould reduce y (2) V=klc" It will now be shown, how this relation can be obtained by the inherent action of the nerator itself without any resistance regu- Eldon or other adjustment.

Figure 1 is a conventional illustration of 'the constant voltage system in accordance with my invention. r 2 illustratesgraphically the relations betweenfield stren h and magneto motive fOl'CB- In'Fig 1 the armature 1 of the generator is acted on by twoop OSGdgfiOldS' 2 and 3, the one being satura ,the other beingunsaturated. These fields are excited from a generator 4 whose speed of rotation isprd portional to that of the armaturel and.

- length, as is welllrnown.

. UNITED STATES PATENT OFFICE.

THOMAS SPENCER, OF PHILADELPHIA, PENNSYLVANIA, ASSIGNOB TO HELIOS MANU- FACTURIN G COMPANY, OF PHILADELPHIA, PENNSYLVANIA, A CORPORATION OF Specification of Letters Patent. P atented Liar, 2'1, 1917 Application filed December 1, 1913. Serial Ho. 80: t,899.

which preferably is directly connected to the armature shaft as shown. The. fields 2 and 3 can be connected either in series or in parallel, the series ct nnection being preferable.

The field 5 of the exciter 4 is energized from some source of constant E. M. F. 6-, preferably a storage battery. The commutator 7 of the main generator 1 is connectedto the lights 8 or other translatin devices directly through the usual automatic switch 9 which is preferably located within the casing of the generator. 1. switch 10 and the two leads 11 and 12, permit the charging of the storage battery fl( an the generator terminals whenever-necessary. This may be accomplished automatic: illy or otherwise, but as it forms no part of my invention, it has not been illustrated on the drawing.

The saturated '1 ield 2 predominates over the unsaturated field 3 and the latter by its opggsition causes a resultant field to. be pro dn (1 that can be proven to vary inversely as the speed of rotation of the main annature. In the arran gement shown, the voltage of the exciter 4 vs 'riesdirectly as the speed of rotation of the armature 1 since thestrength of its field 5 is always constant. The ampere turns on the fields 2 and 3 will therefore vary directly witfiithe speed of rotation of the main generator armature. Since the directioi of the field 5 is always the same, the direczion of the terminal voltage of the exciter L reverses every time the direction of rotation is reversed. The current through the co ils on fields 2 and 3 being reversed whenever the direction of rotation of armature 1 is reversed, the terminal voltage of'the main generator will therefore be unidirectional regardless of the dirwtion in which the car is mo ring. It will thus be seen that one'of the requirements of the previously mentioned idoal car lighting system is fulfilled by the sy;tem described. It will now be proven that the terminal volta e of the system shown is independent 0- the speed.

In Fig. 2 a magnetization curve is shown in which the ordln ates represent field flux per unit area and the abscissas magnetomotive force or ampere turns per unit of It was ointed out a long time ago by Lamont and rolich that such a curve is substantially an equilateral hyperbole represented by the equation am (3) l+bx where w is the magnetizing force which may be expressed in ampere turns per unit length,.y the flux per unit area and a and b are constants. While this equation can be made to coincide with any magnetic curve by properly choosing the constants a, and b, it is of such a form as not to lend itself to the demonstration of the theory of my invention. Any given portion of the magnetization curve however, can be represented by the following equation where a and d are constants and y and a: field strength and ampere turns respectively. By choosing certain values for 0 and d, this curve closely follows any given portion of the magnetization curve, that'is if equation (4) represents that portion of the curve between A and B of Fig. 2, then by choosing other constants, the equation 0 will represent that portion of the curve be tween the points C and D.

' Returning to the system shown in Fig.1,

the field 3 is to be so wound and proportioned that it will work between the limits AB of the magnetization curve while field 3 will be designed to work between limits CD.

It is the usual practice to use storage batter ies for the lights when the cars are standing 40 still or traveling below or above certain limits of speed, the upper and lower. limits being usually 20 and 80 miles per hour respectively. It is therefore obvious that the points A and Ben the one hand and C and 5 D on the other represent the cutting in and cutting out speeds respectively;

' Let 2: represent the ampere turns-on the field 3 for the point A, and fa) the ampere turns for the same field at the point B. If-

the generator is cut in at 20 miles an hour and out out at 80 miles an hour, it is obvious that the ,constant f is equal to 4. Let it be assumed that the ampere turns on field 2 at the cutting in point. C are m times as great as the ampere turns on field 3 at cutting in point A. Therefore the ampere turns on field 2 at the cutting out point D will be m times as great as those on field 3 at cutting out point B, that is the ampere 0 turns will be mfm at this point. With the am ere turns on the two fields thus related, eac point on the curve CD will be 'm times as reat as some point on the curve AB.

aking the previously assumed values for '66 the magneto-motive forces on the two fields,

the equation for that 'mrtion of the curve between A and B is represented by equation (4), and the equation for that portion of the curve between points C and D will be,

is) y C mm If equation (4) be multiplied by some constant k and subtracted from equation (6), the following will result,

Since is is an assumed constant, it is evident that it can be made to have any value desired. It. will, therefore, be assumed that and by substituting this value in equation (7), the following is obtained the terms 0 and 0 having disappeared.

Since is, (Z, d and m are all constants and since kg is the resultant field acting on the main generator armature, the equation reduces to showing that in the described arrangement the resultant field varies inversely as the speed, the ampere turns a: being proportional to the speed.

The constant is by which the equation of the unsaturated field 8 is multiplied merely indicates that the core section of this field is In times the core section of the other field. The accuracy ofthe theory depends, of

course, on the closeness with which the equations represent the portions of the ma netization curve chosen, but since the slig t error in each portion is in the same dlrection,

the variations ofthe two fields to a'certain' theory, a magnetization curve for cast steel given by S. l --Thompson in his dyanmo design will be taken as a typical curve. Taking from this curve the abscissa for the point A as 6.5, the ordinate will be 30,000 lines. The abscissas of point B will. be 7 times this or 26 (f being previously chosen as 4) and the ordinate for this point as taken from the curve is 86,500. Since the abscissa of point C is m times that of point A, and arbitrarily choosing the value of m as 10, theabscissa ofO will be 65, While theordinatc taken from the curve will b8--l05-,500.

Since the abscissa of point D is mi times that of'lpoint B, it will be equal to 260, and'the ordinate taken from the curve will be I26,- 000. In Fig. 2 of the drawing and in the calculations further on, the values of the ordinates have all been divided. by 1,000 for convenience.

Since the equation for that portion of the curve between A and B holds for all the points, the values of the constants c and d can be found by substituting in the equation the values of the coordinates at points A and B. It will then be found that c=105.3 and ai -489.7. Since equation (6) holds for all pointson the portion CD, the values of c andd can be found by substituting the values of the coordinates of C and D in the equation. It will then be found that 0': 132.8 and d=1776.6. Since its value will be 1.261. That is, the field strength of the unsaturated field 3can be multiplied by factor k by makin its core section 1.261 times that of satura field 2.

Taking four arbitrary points on the curve corresponding to the speed of 20 miles, 40 miles, 60 miles and 80 miles, the abscissas of the two intermediate points E and F on the curve for the unsaturated field will be 13 and 19.5 respectively, and the ordinates taken from theThompson curve for such values of magneto motive force will be 62.7 and 78 respectively. In like manner the abscissas for the two intermediate points G and H on the curve for the saturated field will be 130 and 195 respectively while the ordinates taken from such magneto motive force values on the Thom n curve will be 113 and119.5 respective y. With the coordinates of the two limiting s eeds and the two intermediate speeds being thus established for both curves, the values of the resultant field actin on the armature at each of the four points will be determined from the equations and also from flux values taken directly from the 'Thompson curve to show how close the agreement is. i

The value of the resultant field as derived from equation 8 for the four speeds 20, 40,

60 and 80 miles will be 67.67, 33.83, 22.55,

' 16.92. respectively. Now using flux values from the Thompson curve v the field flux 30 at the point A multiplie by thearea factor, 1.261 from the field flux 105.5 at the point C and doing likewise for each of the other speeds, 40, 60 and 80 miles per hour, the resultant field for each of the four points is 67.67, 33.94, 21.14 and 16.92 respectively. It will thus be seen that the e nation is very close to being correct for all points chosen. This means that the voltage can be maintained substantially constant at allspeeds between the assumed speeds of been made to have the curve speed of the armatu re.

and subtracting 20 and 80 miles at hour without any regulw.

tion whatever.

It will be understood that the limitin speeds 20 and 80 miles per hour are used only by way of example. The invention can of. course, be used ivith systems having other constant value.

Hysteresis can lave no appreciable effect on t e operation as a metal can be chosen that has negligible hysteretic properties. An instance of such is cast steel whichis usually used in field cores for train lighting generators especially.

Armature reaction due tothe load can be overcome in my invention in' the same manner as in other sysl ems by the use of appropriate interpoles as well as by other arrangements. I

In Fig. 2 of the drawin no attempt has drawn to scale as it is illustrative only. The coordinates of the eight points an taken from the Thompson curve and are not scaled ofl"f rom Fig. 2.

Fig. 1 is merely a conventional showing of the system and it will be understood that in practice the fields 2 and 3 will each consist oi 95 tion of an armature with a saturated field core adapted to senl flux through the commutated coilsin ore. direction, an unsaturated field core adapted to send field flux simultaneously thro'lgh the said coils in the opposite direction, said cores having sub stantially similar magnetization curves, and means adapted to produce in each core a magneto motive force proportional to the 2. In a generating system, the combination of a rotatable armature with a saturated field core, a second unsaturated field core, said cores having substantially similar magnetization curves, tle flux from said-cores adapted to induce op posed FQTS simultaneously in the same coils of said armature, field coils on each core, and"airenciteri"having a constant field, connected to said armature to rotate therewf th and electrically connected to said coils to saturat'e'one core and undersaturatethe other. a

3. In a generating ;ysteml,the*combination of a rotatable armature with a'saturatcd 6 field core, a second .msaturated field col re", said cores having substantially similar magnetization curves, the flux from said cores adapted to imluceopposed E. M. F.s simultancously in the same coil of said no armature, field coils on each core, a'. generator having a constant field and an armature connected to rotate with the first armature and electricall connected to said coils to saturate the said first core, and undersaturate the second core, the total flux of said second core being less than thatof the 4. In a generating system, the combination of a rotatable armature with a. saturated field core, a second unsaturated field core,

said cores having substantially similar magnetization curves, the flux from said cores :adapted to induce opposed E. M. F.s simultaneously in the same coil of said armsture, field coils on each core, asecond armature connected to rotate with the first armature, a field core therefor, means to produce a substantially constant flux in said third field core, said second armature bein electrically connected in series with said field coils to saturate the firstfield core and undersaturate the second with a lesser flux.

In testimony whereof, I hereto afiix my signature.

THOMAS SPENCER.

Witnesses:-

C. W. GULDEN, HERMAN T. GRUNINGER. 

